Hi Marija Z,
Thank you for querying in this forum.
According to your description, the error message appears when you try to fill the info path form in SharePoint Online.
Sorry for the inconvenience caused at your end. I understand this issue has affected your daily work and apologize for it.
I notice you mentioned service incident on SharePoint Online, so I also go to check the current service incidents, but I don't find any incidents related to info path form. I'm afraid this issue may not be caused by service incident.
I also wish to try my best to help you. I searched a lot about the error message you shared. This error may be caused by that the limitation data connection response size is set to 1500kb for Form Services.
Here are some similar threads for reference:
The amount of data that was returned by data connection has exceeded the maximum limit that was configured by server admin
Log ID:7894 - The amount of data that was returned by a data connection has exceeded the maximum limit
If you need further help about this issue or want to know more details about it, we have a specific channel Microsoft Q&A community handling info path related queries, to make sure you get the dedicated support, I sincerely recommend you post this question in that community, members and engineers in that community are proficient in the knowledge of info path, and they will also focus on your specific situation and provide specific suggestions.
Your patience and understanding are highly appreciated.
Hope you have a safe and happy new year!
Best regards,
Tina